RI validity is determined by how many results fall outside the proposed RI?

• A. 0-2
• B. >4 results --> determine de novo RI
• C. 3-4 fall outside the proposed RI
• D. All results fall outside the proposed RI

Answer: (A)

What’s being tested is how well a proposed reference interval fits the healthy population. In reference-interval validation, you apply the interval to a new set of presumably healthy individuals and see how many results fall outside that interval. If only a couple of results sit outside (often 0–2 in a typical validation sample), the interval is considered valid for the target population. If more than that, the interval likely doesn’t capture the healthy range and should be revised or re-established de novo. So the best standard criterion is that 0–2 outside values indicate a valid RI, while more outside values indicate the need for adjustment.